Now, through an insider close to Toyota, we can reveal more details of the common platform and powerplant cars to be shared by the all-new Toyota Supra and next-generation BMW roadster around the same size as the current Z4.

Both sports cars are due to appear within three years and, while BMW has taken the lead in the packaging and design of both cars, Toyota will add its own styling to the company's new sports flagship, which was loosely previewed by the striking FT-1 concept at this year's Detroit motor show.

According to Japan’s Holiday Auto magazine, the design of the Z4 replacement's body is taking priority in the creative process, and hence stylists are focusing on perfecting a convertible design.

As expected, BMW is incorporating its newly accumulated knowhow in body construction using a hybrid steel and aluminium platform design and carbon-reinforced plastic body panels from the new i-cars to minimise weight and maximise rigidity, performance and efficiency.

This combination forms the basis of the collaborative effort in which the born-again Supra will benefit from BMW’s cutting-edge construction. Given the Z4 successor is being developed as a convertible, it stands to reason that the Supra will follow in the BMW’s footsteps.

While the Supra’s final exterior design not yet been frozen, our source confirms out that the radical FT-1 will bear little resemblance to Toyota’s final design, as suggested by this rendering from Holiday Auto.

Our sources also insist that the Toyota's engine and transmission will be supplied by BMW and that a turbocharged 2.0-litre inline four-cylinder unit will be the main powerplant.

In the Toyota, the direct-injection turbo-four will be paired with the Japanese car-maker's latest 'super conductor hybrid' technology, making the flagship sports car a plug-in hybrid delivering upwards of 260kW.

Hints for this state-of-the-art hybrid powertrain and its front-mounted electric motor can be found in the Yaris Hybrid R Concept revealed at last year’s Frankfurt show.

A more advanced system was employed on Toyota’s TS040 Hybrid race car, which competed in this year’s Le Mans 24-hour.

This car incorporates a motor-generator mounted on the front axle, along with one in the rear. The two units scavenge energy by applying braking force during deceleration to generate current that it sends to a super-capacitor.

The super-capacitor then reverses that flow of power during acceleration, boosting the performance of the internal combustion engine's power delivery. We can expect to see a toned-down version of this system on the road car that – in a first for Toyota – will feature a dual-clutch automated manual transmission.

Effectively making it all-wheel drive (apparently contradicting recent confirmation by chief Toyota 86 engineer Tetsuya Tada that it will be rear-drive, the new Supra will employ three electric motors -- two at the front and one at the rear -- with the front units incorporating a torque vectoring mechanism.

From what we are hearing, the Supra will only be fitted with the plug-in hybrid turbo powertrain, and will not be offered with the BMW’s standard turbo-petrol option, which makes sense given Toyota’s hybrid focus and its desire to differentiate the Supra.

As we've reported, the electric motors will be designed by Toyota but built by BMW, and both cars have a target weight of less than 1400kg.

The 'BMW Supra' was born from a technology sharing deal announced by the German and Japanese companies in 2011, when they confirmed a number of projects including hydrogen fuel cell development.

Effectively, like its successful smaller sports sibling (the Subaru Impreza-based Toyota 86), the new-generation Supra will employ a platform and engine developed by another car-maker – in this case BMW – with Toyota flavour coming courtesy of exterior design, powertrain tech, chassis tune and badging.

Expect to see both joint-venture sports cars in showrooms by the end of 2017.

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